1. Field of the Invention
The present invention relates to radio frequency technologies, and in particular, to a system and method for positioning using signal transmit power and signal receive packet error rate (PER).
2. Description of the Related Art
The conventional radio frequency positioning technologies, besides commonly used global positioning system (GPS), include radar positioning, radio directional positioning, received signal strength indication (RSSI) positioning, radio frequency signal, time of arrival (TOA), and time difference of arrival (TDOA) positioning.
The GPS first needs a GPS satellite receiving terminal for receiving signals from satellites. After calculating the longitude and latitude of a position, the GPS receiving terminal transmits the data to the positioning management center over the mobile communication network, and displays the position on the electronic map. Obviously, the GPS receiving terminal and mobile communication terminal are costly, large, and energy-consuming, which is not suitable for low cost applications. In addition, the GPS is not in full play in a downtown area with a high density of buildings, inside the buildings, and underground mine.
A radar positioning system uses radars to transmit signals along different directions, and determine the position of the search target by analyzing signals returned from the search target. A typical example is using military radars to search for the enemy plane. This is not suitable for positioning applications requiring low cost because the devices are expensive devices and large in size.
Conventionally, for victims in distress occurred on land or on the sea, radars are conditionally used for positioning the big ship in distress and important shipwreck. In case of common small ships without GPS and marine satellite communication devices, or connectionless ships, drowning victims, victims in field distress on land, rescue ships or helicopters are usually used to search for victims by naked eyes. This is very difficult in rescuing, especially in frog and the night with a low visibility.
The radio directional positioning system requires that a simple radio signal generating apparatus be arranged in the search target for intermittently transmitting signals. The searcher needs to determine the position of the signal source using the directional antenna and intercepting device so as to determine the position of the search target according to the signal strength. This method is simple, but is not accurate.
As the development of technology, currently most micro-power transceivers using a single chip support the received signal strength indication (RSSI) function. Therefore, the position of a moving target can be determined based on the obtained signal strength, which has become a most-researched positioning method. This method is simple and requires no additional hardware. However, the RSSI produces a great error in signal strength test and there are many factors affecting the test. Therefore, such signal strength test is far from accurate, especially in small-scale and short-distance positioning.
In addition, the conventional simple positioning technology (see related documents for accurate positioning using the active RFID tag in IEEE and ISO-RTLS international standards ISO/IEC24730-2), positioning is usually achieved by analyzing the received active RFID tag signals. To save energy and reduce the cost, most active radio frequency identification (RFID) tags work at a predetermined transmit power to periodically transmit signals at a predetermined interval. The same RFID tag works in a variety of environments, large or small and with different open spaces. Therefore, if the RFID tag cannot adjust its transmit power according to the working environment to prevent impacts caused by signal blockage and reflection, but transmits signals at the predetermined transmit power. This affects the positioning.
The positioning is achieved by measuring the TOA between the search target and radio frequency signals to the intercepting receiver. Because there is a high requirement on time synchronization between the signal source and signal receiver, this method is not practical. As regards the positioning by measuring the TDOA between the signal source and signal receiver in case of different signals (radio frequency signal and ultrasonic signal), the cost is increased because two different signals are required. That is, two types of signal transmitting devices and receiving devices are required, such as ultrasonic generating device and receiving device. In addition, with this method, the positioning accuracy is closely related to the precision in time difference test, which increases its application complexity and hinders its application.
Although ensuring safety in the underground mine and rescuing the victims in distress are two top issues for safe production in underground mine, only the area where the workers in the underground mine can be determined, far from accurate positioning. Accordingly, in the event of an accident, the victims cannot be accurately positioned, which increases complexity of the rescue work. Therefore, accurately positioning the workers trapped in the underground mine is a critical problem to be solved. In the search and rescue in 5.12 Wenchuan Earthquake, since the position of the trapped plane is difficult to be determined, a large amount of manpower, material resources, and time are used for rescue. This reflects the situation of the current long-distance search and rescue.
To sum up, the conventional positioning technology encounters problems such as high cost, weak practicality, and low positioning precision. Therefore, an economic, precise, simple but efficient positioning technology is desired.